The use of carbon fiber/carbon matrix composite disc brakes, commonly referred to as carbon/carbon composite disc brakes in the aircraft industry is extensively known. Thermal characteristics and the braking efficiency of such braking systems account for their wide spread acceptance. However, those skilled in the art realize that carbon/carbon composite brakes are expensive, a large portion of the costs incident thereto being the labor intensity required in the manufacture of the carbon/carbon composite discs themselves. Carbon/carbon composite brake discs are formed of fibers which are provided in the form of a tow (bundle of continuous filament) or in a roving (a bundle of many short filaments). These fibers may be derived from either pitch or PAN. Those skilled in the art readily understand that pitch fiber is one in which a thermoplastic derivative of coal tar or petroleum pitch is spun into fiber which is subsequently carbonized by an appropriate technique or method for driving the volatiles therefrom. Poly acryol nitrile filgers, commonly referred to as PAN fibers, are oxidized, carbonized, and appropriately heat treated. Both pitch and PAN fibers are well known and extensively used in the manufacture of carbon/carbon composite discs for aircraft braking systems.
The state of the art for the manufacture of carbon/carbon composite discs for the aircraft industry is fairly shown in Pat. No. 5,686,117. There, an effective method and apparatus for forming such carbon/carbon composite discs is shown. However, the technique of that patent typically requires the use of a resin binder in combination with such fiber. When a resin binder is used, it is necessary to subject the resulting disc to a carbonization step such that the resin itself can be carbonized. If the resin binder can be eliminated, such that the disc itself is formed of carbonatized material, the carbonizing step can be eliminated along with the resins. It will also be appreciated by those skilled in the art that some aircraft brake applications are not conducive to implementation with carbon discs which include a resin base. Resin char is low density carbon and, accordingly when resin is employed, density of the resultant disc is sacrificed. Since mass and density are of paramount importance in the context of brake discs, the reduction or elimination of resin content is most advantageous.
It has further been known that in the prior art processes of manufacturing carbon/carbon composite discs the fibers are typically laid in the radially/circumferentially oriented plane so that the resulting disc is layered or stratified with respect to the fibers themselves. In other words, few if any fibers pass in the axially oriented plane with respect to the disc. As a consequence, structural integrity of the disc is sacrificed. Accordingly, it is most desired that the fibers used in construction of carbon/carbon composite brake discs lie in radial, circumferential and, axial directions within the discs. This feature can be achieved by needling of the disc prior to densification or carbon vapor infiltration. However, it is well known in the art that carbonized fibers such as the PAN or pitch fibers typically employed in carbon/carbon composite brake manufacturing are not conducive to such needling. In short, carbonized fibers are generally brittle and not given to ease of reorientation from a radial/circumferential plane to an axial plane.
There remains a need in the art for a method and apparatus for making carbon/carbon composite discs for aircraft brake assemblies which use carbonized fibers in a needled mat or preform and to do so without the use of resin binders.